Electrical parameters of conductive structures contained in printed wiring boards, packages or integrated circuits are determined with suitable electrical measuring instruments like Vector Network Analyzers, Spectrum Analyzers, TDR instrumentation or oscilloscopes. The disadvantage of these electrical measuring instruments, particularly at high frequencies e.g. in the GHz range can be the measurement uncertainty in general and the influence of the contact or the probe of the measurement instrument on the measurement result. Furthermore, no partial conductive structures of the assemblies can be measured contactless with the above mentioned electrical measuring instruments. With the method and apparatus described below these technical problems tend to be solved.